The present invention relates to inkjet printheads. In particular, it relates to a heater chip thereof having a doped diamond-like carbon layer above a resistor layer. More particularly, the doped diamond-like carbon layer includes silicon, nitrogen, titanium, tantalum or other and a cavitation layer of undoped diamond-like carbon, tantalum or titanium overlies the doped diamond-like carbon layer.
The art of printing images with inkjet technology is relatively well known. In general, an image is produced by emitting ink drops from an inkjet printhead at precise moments such that they impact a print medium at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium. It emits ink drops at times pursuant to commands of a microprocessor or other controller. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.
Conventionally, a thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a nozzle or orifice plate attached to the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heaters fabricated by deposition, patterning and etching techniques on a substrate such as silicon. One or more ink vias cut or etched through a thickness of the silicon serve to fluidly connect the supply of ink to the individual heaters.
To print or emit a single drop of ink, an individual resistive heater is uniquely addressed with a small amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local ink chamber (between the heater and nozzle plate) and be ejected through and projected by the nozzle plate towards the print medium.
Heretofore, conventional heater chip thin films on a silicon substrate comprise silicon nitride (SiN) and silicon carbide (SiC) overlying a resistor layer for reasons relating to passivation. Thereafter, a cavitation layer overlies the two passivation layers to protect the heater from corrosive ink and bubble collapse occurring in the ink chamber. In terms of thickness, the SiN is often 2000 to 3000 angstroms, the SiC is 1000 to 1500 and the cavitation layer is 2000 to 4000 angstroms. Thus, at a minimum, the three combined layers above the resistor layer constitute a thickness of several thousand angstroms. Moreover, since all three layers have different chemical compositions, no less than three processing steps are required.
Accordingly, the inkjet printhead arts desire optimum heater chip configurations requiring minimum processing steps without suffering a corresponding sacrifice in printhead function or performance.
The above-mentioned and other problems become solved by applying the principles and teachings associated with the hereinafter described inkjet printhead heater chip having a doped diamond-like carbon thin film layer and overlying cavitation layer.
In one embodiment, a heater chip has a silicon substrate with a heater stack formed of a plurality of thin film layers thereon for ejecting an ink drop during use. The thin film layers include: a thermal barrier layer on the silicon substrate; a resistor layer on the thermal barrier layer; a doped diamond-like carbon layer on the resistor layer; and a cavitation layer on the doped diamond-like carbon layer. Together, the two doped diamond-like carbon and cavitation layers serve the tri-functions of enhanced adhesion, passivation and protection from cavitation. The doped diamond-like carbon layer preferably includes silicon but may also include nitrogen, titanium, tantalum or other. When it includes silicon, a preferred silicon concentration is about 20 to 25 atomic percent. More preferably, it is about 23 atomic percent. A preferred cavitation layer includes an undoped diamond-like carbon, tantalum or titanium layer. The doped diamond-like carbon layer ranges in thickness from 500 to 3000 angstroms. The cavitation layer ranges from 500 to 6000 angstroms. Thus, the combined thicknesses can range from as few as 1000 angstroms to 9000 angstroms.
In another aspect of the invention, the doped diamond-like carbon layer becomes formed on a substrate in a conventional PECVD chamber with a 200 to 1000 volt bias between the substrate and gas plasma. Preferably, the gas plasma includes methane and tetramethylsilane gasses.
In still another aspect, printheads containing the heater chip and printers containing the printhead are disclosed.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in the description which follows, and in part will become apparent to those of ordinary skill in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.